Preheat oven to 350 degrees. Butter a 10 x 13" pan well and set aside.

Cream together the butter and brown sugar until light and fluffy. Add the egg yolk and vanilla and mix well.

In
a separate bowl, whisk together the flour and salt. Add dry ingredients
to the wet ingredients and blend until a soft dough forms. Press down
down into your prepared pan and prick all over with a fork.

Bake for 18-20 minutes until golden brown. Remove from oven and let cool completely before proceeding.

Once
your base has cooled, melt your chocolate chips either in a double
boiler or a microwave-safe bowl, stirring in 30 second increments until
completely melted and smooth. Spread chocolate on cookie base and
scatter nuts on top. Place in fridge for 1 hour until chocolate has set,
then cut into bars!